1. Field of the Invention
The present invention relates to a transmitting and receiving apparatus arranged in a mobile wireless installation or the like.
2. Description of Related Art
FIG. 1 is a constitutional diagram showing a conventional transmitting and receiving apparatus. In FIG. 1, 1 indicates an antenna, 2 indicates a duplexer (hereinafter, called DUP) for outputting a reception wave Rx received in the antenna 1 to a receiving unit 9 and outputting a transmission wave Tx output from a transmitting unit 14, 3 indicates a carrier wave generating unit for generating a reception carrier wave L0 having the same frequency as a reception frequency f.sub.RX of the reception wave Rx and generating a transmission carrier wave L1 having the same frequency as a transmission frequency f.sub.TX of the transmission wave Tx, 4 indicates a local oscillating unit, indicates a phased-lock-loop (hereinafter, called PLL) for generating the reception carrier wave L0 having a frequency f.sub.L0 (=f.sub.RX), 6 indicates a distributing unit for distributing the reception carrier wave L0 generated in the PLL 5, 7 indicates a PLL for generating a signal of which a frequency is equivalent to a difference value between the frequency f.sub.RX and the frequency f.sub.TX, and 8 indicates a mixer (hereinafter, called MIX) for mixing the signal generated in the PLL 7 with the reception carrier wave L0 and outputting the transmission carrier wave L1.
Also, 9 indicates the receiving unit for mixing the reception carrier wave L0 generated in the carrier wave generating unit 3 with the reception wave Rx and outputting reception signal, 10 indicates an amplifying unit for amplifying the reception wave Rx, 11 indicates a band pass filter, 12 indicates a filter for removing higher harmonic waves from the reception carrier wave L0 generated in the carrier wave generating unit 3, and 13 indicates an MIX for mixing the reception carrier wave L0 with the reception wave Rx.
In addition, 14 indicates the transmitting unit for mixing the transmission carrier wave L1 generated in the carrier wave generating unit 3 with the transmission signal and outputting the transmission wave Tx, 15 indicates a filter for removing higher harmonic waves from the transmission carrier wave L1 generated in the carrier wave generating unit 3, 16 indicates an MIX for mixing the transmission carrier wave L1 with the transmission signal, 17 indicates a band pass filter, and 18 indicates an amplifier for amplifying the transmission wave Tx.
Next, an operation is described.
In this transmitting and receiving apparatus, the transmission of the transmission wave Tx and the reception of the reception wave Rx are simultaneously performed. However, a direct converter method is adopted to reduce both a size of the receiving unit 9 and a size of the transmitting unit 14. In this direct converter method, the reception wave Rx is directly converted into the reception signal of a desired frequency, and the transmission signal is directly converted into the transmission wave Tx of a desired frequency.
More precisely, the reception carrier wave L0 having the same frequency as the reception frequency f.sub.RX of the reception wave Rx is generated in the carrier wave generating unit 3 to directly obtain the reception signal of the desired frequency from the reception wave Rx.
Thereafter, when the reception carrier wave L0 of the frequency f.sub.L0, which agrees with the reception frequency f.sub.RX, is generated in the carrier wave generating unit 3, the reception carrier wave L0 is mixed with the reception wave Rx in the receiving unit 9, and the reception signal is output from the receiving unit 9.
Therefore, the reception signal of the desired frequency can be taken in.
Also, because the transmission carrier wave L1 having the same frequency as the transmission frequency f.sub.TX of the transmission wave Tx is generated in the carrier wave generating unit 3 to directly obtain the transmission wave Tx of the transmission frequency f.sub.TX from the transmission signal.
Thereafter, when the transmission carrier wave L1, of which the frequency f.sub.L1 agrees with the transmission frequency f.sub.TX, is generated in the carrier wave generating unit 3, the transmission carrier wave L1 is mixed with the transmission signal in the receiving unit 14, and the transmission wave Tx is output from the transmitting unit 14.
Therefore, the transmission signal Tx of the transmission frequency f.sub.TX can be transmitted.
Because the conventional transmitting and receiving apparatus has the above-described configuration, the size of the receiving unit 9 and the size of the transmitting unit 14 can be made small. However, because the frequency f.sub.L0 of the reception carrier wave L0 agrees with the reception frequency f.sub.RX, the reception carrier wave L0 leaks out to a front end unit (the antenna 1 and the DUP 2) and functions as interference wave. Therefore, there is a problem that a DC offset occurs in the reception signal.
Also, because the frequency f.sub.L1 of the transmission carrier wave L1 agrees with the transmission frequency f.sub.TX, the transmission wave Tx leaks out to interfere with the carrier wave generating unit 3. As a result, there are following problems. That is, the transmission carrier wave L1 become unstable, a modulation precision of the transmitting unit 14 becomes worse, floor noise occurring in the modulating unit is increased, and electric power cannot be reduced in an electric power control operation which is performed in a CDMA or the like.